In January 1986 the first ever computer virus was unleashed via floppy disk, and 20 years on the problem is still very much a nightmare situation for the average PC user.
Though it's origin is still disputed it is thought the virus, known as Brain, was coded by two Pakistani programmers named Basit and Amjad who designed their virus to affect every 360kb floppy inserted into the drive. Four years later a company called Symantec launched the now hugely popular Norton Antivirus.
Within two years the number of malicious programs had increased by 420% to 1300, this was probably helped by creation kits like the Virus Creation Laboratory which was also released in 1992.
Some of the more memorable viruses since then include 1999's Melissa virus, which executed a macro which sent copies of itself to 50 people in the users Outlook address book, the Love Bug which deleted MP3, MP2 and JPG files as well as sending usernames and passwords to the author and 2004's MyDoom worm which affected businesses, banks and the British Coastguard.
Today there are more than 150,000 malicious programs and over 25 major companies specialising in anti-virus software for the Windows platform alone.
View: Computer Virus Timeline